3.21 Operators

op(+Precedence, +Type, +Name)

Declare Name to be an operator of type Type with precedence Precedence. Name can also be a list of names, in which case all elements of the list are declared to be identical operators. Precedence is an integer between 0 and 1200. Precedence 0 removes the declaration. Type is one of: xf, yf, xfx, xfy, yfx, yfy, fy or fx. The `f' indicates the position of the functor, while x and y indicate the position of the arguments. `y' should be interpreted as ``on this position a term with precedence lower or equal to the precedence of the functor should occur''. For `x' the precedence of the argument must be strictly lower. The precedence of a term is 0, unless its principal functor is an operator, in which case the precedence is the precedence of this operator. A term enclosed in brackets ( ... ) has precedence 0.

The predefined operators are shown in table 3. Note that all operators can be redefined by the user.

1200	xfx	-->, :-
1200	fx	:-, ?-
1150	fx	dynamic, multifile, module_transparent, discontiguous, volatile, initialization
1100	xfy	;, |
1050	xfy	->
1000	xfy	,
954	xfy	\
900	fy	\+, not
900	fx	~
700	xfx	<, =, =.., =@=, =:=, =<, ==, =\=, >, >=, @<, @=<, @>, @>=, \=, \==, is
600	xfy	:
500	yfx	+, -, /\, \/, xor
500	fx	+, -, ?, \
400	yfx	*, /, //, <<, >>, mod, rem
200	xfx	**
200	xfy	^

Table 3 : System operators

current_op(?Precedence, ?Type, ?Name)

Succeeds when Name is currently defined as an operator of type Type with precedence Precedence. See also op/3.